Detainees held in Afghanistan by American troops have been routinely tortured and humiliated as part of the interrogation process, in the same way as those in Iraq, a Guardian investigation has found.

Five detainees have died in custody, three of them in suspicious circumstances, and survivors have told stories of beatings, strippings, hoodings and sleep deprivation.

The nature of the alleged abuse indicates that what happened at Abu Ghraib prison in Iraq was part of a pattern of interrogation that has been common practice since the US invasion of Afghanistan.

Yesterday, in an attempt to stem charges that senior officials in the Bush admin-istration condoned the use of torture in the war on terror, the White House released hundreds of pages of documents outlining its internal deliberations on interrogation.

The memos, which originated at the Pentagon, the White House and the justice department and date from January 2002 to April last year, were intended to show that the president and his aides insisted that detainees at Guantánamo Bay should be treated humanely.

But one such memo leaked earlier this month said that Mr Bush had the legal authority to allow torture, giving new impetus to a campaign by human rights organisations and Democrats.

Senator Patrick Leahy, the Democratic member of the Senate subcommittee on foreign operations, told the Guardian that prisoners in Afghanistan "were subjected to cruel and degrading treatment, and some died from it".

"These abuses were part of a wider pattern stemming from a White House attitude that 'anything goes' in the war against terrorism, even if it crosses the line of illegality."

Syed Nabi Siddiqi, a former police officer, said he was beaten and stripped. "They took off my uniform. I showed them my identity card from the government... Then they asked me which of those animals - they made the noise of goats, sheep, dogs, cows - have you had sexual activities with?"

A second detainee, Noor Aghah, said he was forced to drink bottles and bottles of water during his interrogation.

Another prisoner, Wazir Muhammad, was held for nearly two years, firstly in Afghanistan and then at Guantánamo Bay.

"At the end of my time in Guantánamo, I had to sign a paper saying I had been captured in battle, which was not true," he said. "I was stopped when I was in my taxi with four passengers. But they told me I would have to spend the rest of my life in Guantánamo if I did not sign it, so I did."

Parts of an inquiry by Brigadier General Chuck Jacoby into allegations of abuse in custody are to be made public next month by the head of the US forces in Afghanistan, Lieutenant General David Barno.

Gen Barno said: "I will tell you without hesitation that intelligence procedures have got to be done in accordance with the appropriate standards _ all our forces will treat every detainee here with dignity and respect."

The network of US detention centres around Afghanistan has largely avoided scrutiny, yet, according to the coalition forces last week, more than 2,000 people have been detained there since the war.

"In some ways the abuses in Afghanistan are more troubling than those in Iraq," said John Sifton of Human Rights Watch. "While it is true that abuses in Afghanistan often lacked the sexually abusive content of the abuses in Iraq, they were in many ways worse.

"Detainees were severely beaten, exposed to cold and deprived of sleep and water. Five are known to have died [two of natural causes]."